So should i go ahead and order one from the ebay link, posted above, for 50 bucks? It says sunfires from 00-05, so I fit in there

 

i wouldn't see why your shouldn't, quite a good price looks like

 

Sorry Typo *Buy the rest from FS including the install, not ebay.

A basic harness is literally a wire adapter; The HU must be wired in to the factory wiring, rather than cutting your factory adapter off which is a total pain in the *** to reverse, you plug in that Scosche harness to your factory harness, the wires from the Scocshe harness are cut/soldered/connected to the Head unit harness which then plugs in to a jack in the back of the HU

More advanced Harnesses have that extra box that has a chip in it that mimics the tasks your old radio used to do that the aftermarket HU does not.

All fairly simple stuff.

Edit: Either Harness will work but I've always been fond of Scosche.